prioritizr (version 4.0.2)

objectives: Problem objective

Description

An objective is used to specify the overall goal of a conservation planning problem. All conservation planning problems involve minimizing #' or maximizing some kind of objective. For instance, the planner may require a solution that conserves enough habitat for each species while minimizing the overall cost of the reserve network. Alternatively, the planner may require a solution that maximizes the number of conserved species while ensuring that the cost of the reserve network does not exceed the budget.

Details

Please note that failing to specify an objective before attempting to solve a problem will return an error.

The following objectives can be added to a conservation planning problem:

add_min_set_objective

Minimize the cost of the solution whilst ensuring that all targets are met. This objective is similar to that used in Marxan.

add_max_cover_objective

Represent at least one instance of as many features as possible within a given budget.

add_max_features_objective

Fulfill as many targets as possible while ensuring that the cost of the solution does not exceed a budget.

add_max_phylo_objective

Maximize the phylogenetic diversity of the features represented in the solution subject to a budget.

add_max_utility_objective

Secure as much of the features as possible without exceeding a budget.

See Also

constraints, decisions, penalties, portfolios, problem, solvers, targets.

Examples

# NOT RUN {
# load data
data(sim_pu_raster, sim_features, sim_phylogeny)

# create base problem
p <- problem(sim_pu_raster, sim_features) %>%
     add_relative_targets(0.1)

 # create problem with added minimum set objective
p1 <- p %>% add_min_set_objective()

# create problem with added maximum coverage objective
# note that this objective does not use targets
p2 <- p %>% add_max_cover_objective(500)

# create problem with added maximum feature representation objective
p3 <- p %>% add_max_features_objective(1500)

# create problem with added maximum phylogenetic representation objective
p4 <- p %>% add_max_phylo_objective(1900, sim_phylogeny)

# create problem with added maximum utility objective
# note that this objective does not use targets
p5 <- p %>% add_max_utility_objective(5000)

# }
# NOT RUN {
# solve problems
s <- stack(solve(p1), solve(p2), solve(p3), solve(p4), solve(p5))

# plot solutions
plot(s, axes = FALSE, box = FALSE,
     main = c("minimum set", "maximum coverage", "maximum representation",
              "phylogenetic representation", "maximum utility"))
# }